While neuronal numbers, dendrites and synapses decline with age and the ventricular volume triples, cerebral circulation is similar to young adults, although there is a reduction in cerebral blood flow (CBF).

The purpose of our study was to investigate the fact that, during aneurysmal surgery, the degree of reducedcerebral blood flow (CBF) and disturbed CO2 responsiveness due to subarachnoid hemorrhage (SAH) were influenced by the elapse of time from SAH to surgery.

In the absence of any significant increase in ICP, cerebral edema appears to cause a significant reduction in cerebral blood flow and this reduction corresponds with the magnitude and location of the edema.